What means exactly adaptive check? It is aktive in my mini.
From the manual
Adaptive Mail Check
When this setting is enabled, the device listens more frequently for a reply to a sent message for ten minutes. If the recipient replies quickly, you can receive the reply before the next scheduled listen interval. This setting is always enabled on consumer and professional flex accounts. On byte-based plans, it can be disabled to reduce battery consumption.
Normally - which is to say when you are not sending messages - the iR devices actively check for inbound messages at power on, whenever they send something (for example, a sent track point or a message) and once an hour. However, when you send a message, the incoming check associated with that send is not sufficient to carry on a "conversation". By the time the recipient of your message sees it and composes a reply, the check associated with the send has long since finished - without seeing the reply. The net result would be that you would not see the reply until the next send, or until the next hourly check rolls around.
The adaptive mail check is designed to solve this problem. When you sent a message (not a track point), the unit listens for 10 minutes after the send. Hopefully, the reply arrives in that time. If you than reply to the reply, the whole process starts again. Net result is a true conversation without undue delays. The downside is that active message checks are expensive from a power perspective.